Radiotelegraph receiver



March 19, 1940. LOWELL 2,193,825

RADIO TELEGRAPH RECEIVER Filed Sept. 11, 19371 SIGNAL MODULATED AT l000- BAND Pass FILTERS r-bo- 7 PERC/VAL D. LOWELL,

Patented Mar. 19, 1940 i UNITED STATES PATENT OFFKIE v RADIOTELEGRAPH RECEIVER Percival D. Lowell, Chevy Chase, Md.

Application September 11, 1937, Serial No. 163,461 7 Claims. (01. 250-4) My invention relates broadly to radiotelegraph tained by starting and stopping the audio frereceiving systems and more particularly to printquency modulation of the transmitter carrier ing telegraph circuits wherein signal pulses in Wave. Two-tone effect at the receiving end using two tones are utilized for operating printing only one on-off tone at the transmitter can be 5 mechanism 1 I Where printing telegraph receivers are instation. In carrying out my invention it is asstalled in connection with systems employing sumed for example that the modulation fretWo-tone modulation at the transmitters, it is quency at the transmitter is 1000 cycles and that only necessary to provide at the receivers seleca superheterodyne type of receiver is employed at attained using my invention at the receiving tive circuits adapted to the two-tone modulation the receiving station. Provisionis made for mod-- 10' employed. Many transmitters, however, emit ulating the frequency converting oscillator at a signals constituted as a carrier wavemodulated frequency of, for example, 1500 cycles, by means by only a single tone in on-off fashion, making of an external audio frequency tube generator. up the signal in combinations of pulses and Following the circuit through, where a mark '15 spaces. Ordinarily it is not possible to operate impulse is being transmitted, the carrier ismod- 115' printer mechanism requiring two-tone signals ulated at 1000 cycles and the received signal goes by any other type of modulated wave. through the receiver in a normal manner,

One of the objects of my invention, therefore, through an audio frequency 1000 cycle band is to provide an arrangement for simulating pass filter and rectifieri The output of the rectwo-tone modulation in the output of a radiotifier is fed to one winding of a polarized relay telegraph receiver when the signal input is of and causes the armature to pull to the marking the single tone, err-off modulated type. side. The output of the rectifier is also fed into Another object of my invention is to provide the grid return circuit of the 1500 cycle audio a tone generator operative at a frequency diffrequency tube generator in such a way that the ferent from the tone frequency of modulation in grid becomes highly negative causing the cir- 25 the received signal and means for impressing the cult to stop oscillating. Then the frequency conoutput of such generator on the carrier wave in vetting oscillator is not modulated. When the the intervals between the modulations thereof 1000 Cycle modulation of the s er s ein order to produce the effect of two-tone modumoved for a space impulse, there will be no lation of the carrier. 1000 cycle signal to go through the 1000 cycle 30 Still another object of myinvention is to profilter and therefore no direct current flow in the vide, in a superheterodyne type of receiver, output of the rectifier and the relay will be unmeans for modulating the output of the conenergized and the negative cut-off bias removed version oscillator at a tone frequency different from the 1500 cycle audio frequency tube genfrom the frequency of the modulation in the crater, allowing it to oscillate. Therefore simul- 35 signal received, in the intervals between recurtaneously, the frequency converting oscillator ring signal pulses. becomes modulated at 1500 cycles, combines with A further object of my invention is to provide the incoming unmodulatcd signal carrier and a a radiotelegraph receiver for single tone modu- 1500 cycle audio frequency signal will pass 40 lated signals with two-tone signal output cirthrough the 1500 cycle band pass filter, be rec- 40 cults, and means for supplying a second tone tified, and excite the relay winding in an oppossignal intermediate pulses of the signal modulaing direction, causing the armature to pull over tions received. to the spacing position. a

Other and further objects of my invention re- Referring more particularly to the drawing, I

side in the circuits and arrangements hereinhave shown first a radio frequency amplifier 45 after set forth with reference to the accompanystage 3 fed from the antenna circuit I through ing drawing which shows by way of example a resonant circuit 2. The output circuit of the schematic diagram of my invention as applied high frequency conversion oscillator 4 is couto the superheterodyne type of radiotelegraph pled together with the output circuit of the amreceiver. The drawing schematically illustrates plifier 3 to the input of the converter of first 50 suchreceiver in outline only, and it will be 1111- detector stage 5. The output of the converter derstood that the various related elements known at intermediate frequency is fed to the second in the art may be added thereto. detector stage 6. -The foregoing broadly states My invention is directed to a printing telethe elements of the superheterodyne receiver as graph system whereby the signal pulses are obdisclosed. 55

In the output of the second detector would appear normally, with single tone modulated signals, recurring pulsations in the signal code and of the tone employed for modulation, a tone of, say, 1000 cycles. Accordingly selective filter and amplifier circuits are provided at l coupled with the second detector 0 and connected with one winding 8a of the polarized relay 8 through a rectifier device 9. The relay 8 will be operative, however, only in one direction, with the recurring signal pulses at 1000 cycles.

In order to operate the relay 8 properly, as with two-tone signal transmission, I provide an audio frequency oscillator circuit 10 arranged to modulate the output of the high frequency conversion oscillator 4 at say, 1500 cycles, and selective filter and amplifier circuits l2 coupled with the second detector 6 and connected with the other winding 8b of the polarized relay 8.

through a rectifier device I4. The winding 81) of the relay will thus be energized in accordance with the operation of the audio frequency oscillator H] which supplies the 1500 cycle signal.

As the presence of the 1500 cycle tone is desirable only in the absence of the 1000 cycle signal pulses in order to simulate accurately the two-tone modulation required to efiect proper operation of the polarized relay 8, I provide connections l5 from the output of the rectifier 9 to supply a cut-off potential in the grid circuit of the audio frequency amplifier ID, as illustrated, when current flows in the circuit of rectifier 9. In the absence of such current, which is the condition between 1000 cycle signal pulses, the audio frequency oscillator circuit H] has correct operative potentials supplied thereto and accordingly functions to provide a 1500 cycle signal which results in a current flowing in the circuit of rectifier l4 and winding 8b of the polarized relay.

In the absence of a carrier wave resonant in circuit 2, the output of audio frequency oscilllator ID continuously modulates the conversion oscillator 4; but as the frequency of the oscillator 4 differs from the intermediate frequency of the superheterdyne system, the modulated output of the oscillator is confined to the circuits of the first detector stage 5 and no current will appear in the circuit of rectifier l4, and Winding 8b of the relay. This is a distinct advantage of my system obtainable in the superheterodyne type of receiver as disclosed.

The system of my invention is adaptable to various types of receiving circuits as will be understood by those skilled in the art. For example, the 1500 cycle signal may be produced as a beat note between the local high frequency oscillator and the carrier wave of the received signal, the local oscillator being under the control of the signal modulation of the carrier, as hereinbefore described with reference to the oscillator H1; in a superheterodyne receiver, this high frequency oscillator may beat with the intermediate frequency wave and thus be stabilized at a selected frequency.

Furthermore, in continuous wave reception, I may provide a high frequency beat oscillator for producing with the continuous signals an audible beat of say, 1000 cycles, and an audio frequency oscillator for, say 1500 cycles arranged to oscillate under control of the received signals. In continuous wave reception however, the audio frequency oscillator may constantly supply current to one winding of the relay when not controlled by the beat note, due to the complete cut-off of the carrier between pulses of the continuous wave signals.

Thus while I have described my invention in a preferred embodiment, I desire it understood that modifications may be made in the type of circuit and the circuit arrangements, and that no limitations are intended, therefore, except as imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A radiotelegraph receiving system comprising circuits tuned to resonance with an incoming signal wave, a detector circuit connected with said tuned circuits and having selective circuitscoupled therewith, one of said selective circuits being adapted to pass currents of the frequency of modulation of the incoming signal Wave, means coupled with said tuned circuits for introducing currents of a different frequency for passing which another of said selective cir cuits is adapted, and means energized from the first said selective circuit for controlling the operation of the aforesaid means in accordance with the signal current.

, 2. A radiotelegraph receiving system adapted to provide two-tone signal output from a single tone modulated signal input, comprising circuits for detecting the single tone modulated signal input and a selective circuit coupled thereto for passing currents of the frequency of modulation, means for introducing a second tone signal into said circuits for detecting, a separate selective circuit coupled to said circuits for detecting and adapted to pass currents of said second tone signal, and means energized from the first said selective circuit for controlling the operation and inoperation of the aforesaid means respectively with the absence and the presence of signal currents in the first said selective circuit.

3. A radiotelegraph receiving system adapted to provide two-tone signal output from a single tone modulated signal input, comprising circuits for detecting and selectively passing the single tone signal modulations, and means connected with said circuits for producing a second tone signal in the time intervals between the single tone modulations, said single tone and said second tone signals in conjunction constituting in effect a two-tone signal output.

4. A radiotelegraph receiving system including dual selective circuits at the output thereof adapted for two-tone signal output, local means for producing signals of one tone directly coupled with said receiving system, and means responsive to received signals of the other tone for limiting the operation of said local means to provide signals of the one tone for said two-tone output in the absence of signals of the other tone.

5. A superheterodyne telegraph receiving system including conversion oscillator, first and second detector circuits, dual selective circuits coupled with the second detector circuit adapted for two-tone signal output, means for modulating said conversion oscillator circuit for producing signals of one tone, and means responsive to received signals of the other tone for limiting the operation of said modulating means to provide signals of the one tone for said two-tone signal output in the absence of signals of the other tone.

6. A superheterodyne radiotelegraph receiving system including conversion oscillator, first and second detector circuits, dual selective circuits coupled with the second detector circuit and adapted for two-tone signal output, a low frequency oscillator coupled with said conversion oscillator for modulating the output thereof at the frequency of one of said selective circuits, and means for controlling the operation of said low frequency oscillator in accordance with current conditions in the other of said selective circuits.

'7. A radiotelegrapl'i receiving system as set forth in claim 5 and including a heterodyne oscillator modulated by said local means, a first detector, and intermediate selective circuits responsive at the beat frequency of the heterodyne oscillation and a received carrier Wave in said first detector, whereby the signals of the one frequency produced by said local means are transmitted to the respective selective output circuit with the cooperation of said received carrier wave and are not efiective in said output circuit in the absence of the carrier wave.

PERCIVAL D. LOWELL. 

